Method for estimating cement amount

Abstract

To provide a novel method for estimating a cement amount.SOLUTION: When estimating a cement amount in a cement-containing material, an acid solution is added to the material to dissolve a calcium component, an alkali solution is added to adjust pH, a calcium amount is measured using a calcium ion selective electrode, and a cement amount is estimated according to the obtained measurement value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for estimating the amount of cement mixed into ground, for example, in a ground improvement method or the like. [Background technology]

[0002] In ground improvement methods, it is common to check the hardening after construction by checking the strength of sampled samples. However, cement, which is usually used as a solidification material, takes about one month to develop its final strength, so tests are generally conducted 28 days or more after construction. However, when there is concern about the mixing state of the cement and ground, it is necessary to grasp the mixing state early and to grasp the amount of solidification material containing cement mixed into the ground. Due to this need, a method has been proposed to estimate the amount of cement in the ground mixed with the solidification material, i.e., in the material containing cement.

[0003] One method for estimating the amount of cement includes, for example, the steps of contacting a material containing a solidification agent with an acid, acquiring the time-varying characteristics of pH when the cement in the material and the acid are neutralized, and estimating the amount of cement based on the acquired time-varying characteristics (Patent Document 1).

[0004] However, the standard of pH time change characteristics is vague and time-consuming, and new proposals for methods to estimate the cement content are also desired. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-59851 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to propose a new method for estimating the cement amount. [Means for solving the problem]

[0007] The means for solving the above problem is In estimating the cement content of materials containing cement, Adding an acid solution to the material to dissolve calcium; Add an alkaline solution to adjust the pH, Calcium levels were measured using a calcium ion-selective electrode. Estimating the amount of cement based on the measurements obtained; The method for estimating the amount of cement is characterized by the following. Effect of the Invention

[0008] The present invention provides a new method for estimating the amount of cement. [Brief description of the drawings]

[0009] [Figure 1] The amount of cement was calculated from the results of atomic absorption spectrometry. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Next, an embodiment of the present invention will be described. Note that the embodiment is an example of the present invention. The scope of the present invention is not limited to the scope of the embodiment.

[0011] In the method of this embodiment, first, an acid solution such as hydrochloric acid is added to a material containing cement to dissolve the calcium content in the cement. Next, an alkaline solution such as sodium hydroxide is added to adjust the pH to a level at which a calcium ion selective electrode can be used. This pH is usually 5 to 11, preferably 6 to 8. After adjusting the pH, the calcium amount is then measured using a calcium ion selective electrode. Then, the cement amount is estimated based on this measured value (calcium amount).

[0012] Although the amount of calcium contained in various cements varies depending on the type of cement, the amount of calcium contained in each type of cement is almost the same. Furthermore, the amount of calcium contained in cement is significantly greater than the amount of calcium contained in general soil. Therefore, by measuring the amount of calcium in a material that contains cement, the amount of cement in that material can be estimated.

[0013] Incidentally, the cement targeted by this embodiment is not limited, and includes cements used in ground improvement methods, such as Portland cement, gypsum, various hydraulic powders (solidifying materials) composed of blast furnace slag powder, blast furnace type B cement, general soft soil cement-based solidifying materials, etc. Also, there is no limitation on materials containing cement, and includes, for example, soil cement, mortar, concrete, etc.

[0014] By the way, pH is commonly known as a method for measuring the concentration of an aqueous solution by measuring the potential difference between liquids. This pH indicates the hydrogen ion concentration in a solution, and is measured by utilizing the fact that the glass membrane potential of a glass electrode is selective for hydrogen ions. Similarly, the amount (concentration) of calcium ions in a solution can be measured by measuring the potential difference using an electrode with a membrane potential selective for calcium ions (calcium ion selective electrode).

[0015] In this embodiment, examples of the acid solution that dissolves calcium include aqueous solutions of hydrochloric acid, sulfuric acid, nitric acid, gluconic acid, etc. In the case of hydrochloric acid, the reaction proceeds as shown in the following formula.

[0016] CaO + 2HCl → CaCl2+ H2O

[0017] Examples of the alkaline solution for adjusting the pH include aqueous solutions of sodium hydroxide, potassium hydroxide, ammonia, sodium carbonate, and the like.

[0018] The cement content can be estimated based on the measured value (calcium content) using the following method.

[0019] One method is to estimate the amount of cement by multiplying the measured amount of calcium by the dilution factor and dividing by the percentage of calcium in each type of cement (estimated amount of cement = measured calcium x dilution factor / percentage of calcium in cement).

[0020] Specifically, for example, if 100 ml of material containing blast furnace type B cement (calcium content 40%) is dissolved in an acid solution, the pH is adjusted with an alkaline solution, and then diluted with water to make 500 ml (5 times dilution), and the calcium content measured with a calcium ion selective electrode is 50 g / L, then: Estimated amount of cement = 50 x 5 / 0.4 = 625 kg / m 3 It becomes.

[0021] In addition, in the case of using this method, it is more preferable to make the following correction. Corrected cement content estimate = Cement content estimate using calcium ion selective electrode (= estimated cement content above) x correction value Here, the correction value = the estimated value using a calcium ion selective electrode / the analytical value using at least one of atomic absorption spectrometry and ICP atomic emission spectrometry.

[0022] In the previous example, if the correction value is 0.9, Corrected cement amount estimate = 625 / 0.9 = 694 kg / m 3 It is.

[0023] This correction is made for the following reasons. The calcium ion selective electrode method takes less time to dissolve calcium than atomic absorption spectrometry, the dilution rate is kept low to minimize dilution errors, and calcium dissolution is suppressed due to the high concentration of sludge discharged. Furthermore, the on-site sample soil is wet and contains water, so it may be diluted more than the dilution rate. In other words, the measurements using the calcium ion selective electrode tend to be lower than those using atomic absorption spectrometry, and by taking into account the above formula (1), it is possible to estimate the cement content more accurately. Another reason for the correction is that when the ground to be improved contains a large amount of shell layers or limestone, positive errors are likely to occur in the estimated cement content.

[0024] Incidentally, in the case of atomic absorption spectrometry, the correction value is, for example, 0.8 to 1.0, and preferably 0.9.

[0025] The next method for estimating the amount of cement based on the measured value (amount of calcium) is to prepare a material containing cement (for example, a sample containing cement made by mixing an earthen material with a solidification material containing cement), create a relational equation between the amount of cement and the amount of calcium for this sample, and estimate the amount of cement by substituting the measured value obtained by a calcium ion selective electrode into this relational equation. This method is useful when a new cement-containing material is the subject of the study and there is no knowledge about the calcium ratio or correction value. The above-mentioned correction can also be made with this method.

[0026] As described above, the estimation method using the calcium ion selective electrode of this embodiment is possible even when the calcium concentration is high, and it is possible to simplify the dilution process and reduce measurement errors. In addition, since the measurement can be performed simply by immersing the electrode in the solution, estimation can be performed very easily. This leads to the miniaturization and simplification of the measurement device. EXAMPLES

[0027] Next, an embodiment of the present invention will be described. (Calcium Determination in Cement Paste) A test was conducted to estimate (calculate) the cement content from the calcium content using the following procedure.

[0028] First, cement (blast furnace type B) and mixing water (ion-exchanged water) are mixed to make the cement concentration 25 to 100 kg / m 3 The solution was adjusted to 100 ml. This solution was stirred for 15 minutes. Next, 10% hydrochloric acid and dilution water (ion-exchanged water) were added to make the volume 400 ml. This solution was stirred for 10 minutes. At this point, the pH (pH after dissolution) was measured. Next, a 6 mol / l aqueous solution of sodium hydroxide was added to adjust the pH to around 7. Next, dilution water (ion-exchanged water) was added to make the volume 500 ml. Next, the amount of calcium was measured using a calcium ion selective electrode. It took 3 to 5 minutes for the measured value to stabilize. The results are shown in Table 1.

[0029] [Table 1]

[0030] (Consideration) If the pH after adding the acid solution is weakly acidic, the calcium will not be sufficiently dissolved from the solidification material, which tends to result in large errors. It was found that by setting the pH to 3 or less, the amount of dissolved calcium increases, making it possible to measure with high accuracy.

[0031] (Calcium determination in simulated sludge) The same tests as those for the cement paste described above were carried out on the simulated sludge. The results are shown in Table 2.

[0032] [Table 2]

[0033] (Consideration) Similar to the results for cement paste, it was found that the amount of calcium elution increased and could be measured accurately by lowering the pH to 3 or less after adding the acid solution.

[0034] (Calcium determination in on-site sludge) The same test as above was carried out on the sludge discharged from the site. However, in this test, the calcium content was measured by two methods: an ion meter (on-site measurement) and atomic absorption spectrometry (later measurement). Specifically, the following was done.

[0035] First, in the case of using an ion meter, 50-100 ml of on-site sludge and 400-600 ml of 10% hydrochloric acid were mixed and stirred for 10 minutes. At this point, it was confirmed that the pH was 2.5 or less. Next, a 6 mol / l aqueous solution of sodium hydroxide was added to adjust the pH to around 7. Next, dilution water (ion-exchanged water) was added to adjust the volume to 1500-2000 ml. Then, the calcium content was measured using an ion meter (meter calibration: 10 g / L, 1 g / L).

[0036] On the other hand, in the case of atomic absorption, 1-3 g of dried sludge was mixed with 200 ml of hydrochloric acid (1+50), stirred, and left for 2 days. After this, the solution was filtered, and the filtrate was diluted to 500 ml, and further diluted 200 times with pure water. Then, the calcium content was measured by atomic absorption. The results are shown in Table 3 and Figure 1.

[0037] [Table 3]

[0038] (Consideration) The reason why the on-site measurements (when an ion meter is used) are lower than the atomic absorption values ​​is as mentioned above. That is, firstly, in the on-site measurements, although a high concentration of hydrochloric acid is used, the calcium dissolution time is shorter than in atomic absorption analysis. Also, in the on-site measurements, the dilution rate is kept low to minimize dilution errors, and the high concentration of the effluent sludge inhibits calcium dissolution. Therefore, it is more suitable to measure the cement content by correcting the on-site measurements by creating a relational equation between the on-site measurements and the atomic absorption measurements, etc. [Industrial Applicability]

[0039] The present invention can be used, for example, as a method for estimating the amount of cement mixed into the ground in a ground improvement method or the like.

Claims

1. In estimating the cement content of materials containing cement, Adding an acid solution to the material to dissolve calcium; An alkaline solution is added to adjust the pH, Calcium levels were measured using a calcium ion-selective electrode. Estimating the amount of cement based on the measurements obtained; A method for estimating a cement amount, comprising:

2. The amount of cement is estimated by multiplying the measured value by the dilution factor and dividing by the percentage of calcium. The method for estimating the amount of cement according to claim 1.

3. A sample containing cement is prepared, and a relationship between the amount of cement and the amount of calcium is created for this sample. The measured value is substituted for the calcium amount in this relational expression to estimate the cement amount. The method for estimating the amount of cement according to claim 1.

4. a relational expression between the estimated value by the calcium ion selective electrode and the analytical value by at least one of atomic absorption spectrometry and ICP atomic emission spectrometry is prepared, and correction is performed based on this relational expression; The method for estimating a cement amount according to claim 2 or 3.

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